A3 Alarm problems

[Mtd]

I have had my A3 for 2 yrs and no problems with the alarm until now. When i lock it up with the remote several minutes or an hour later the alarm will go off for no apparent reason it will also go off even if i dont lock the car up. Then when it goes off i cant switch it off remotely or any other way it seems to have a mind of its own.

[a8 tech]

Possible cause
1 rear washer pipe adrift and leaking washer fluid on to the boot micro switch
2 corrosion of the convenience control unit multi plugs osr D pillar
3 defective alarm siren
4 defective door lock/bonnet lock

I would suggest from your description the fault is a resistive type most likely at the convenience control unit j393 or even the control unit itself


Try establishing the last trigger by looking at measure value blocks in address 46

[Mtd]

Ok thanks for that. Not sure what you meant in the last bit though "Try establishing the last trigger by looking at measure value blocks in address 46"

[a8 tech]

Thats the vag com bit

[pauldazzle]

The most common cause for this problem is the alarm siren box which is located in the near side rear wing underneath the subwoofer. There are 2 batteries in it that after a few years leak onto the PCB, & cause the alarm to go off randomly. I had this happen on my car & took the damn thing out before the neighbours killed me. Your alarm will work normally, but no siren.

[Mtd]

Ok thanks for your help.
I had to disconnect the battery because of the neighbours since i reconnected the battery i have had no problems (touch wood)

[pauldazzle]

I'm absolutely sure it's the alarm siren box that's the source of the problem.

[a8 tech]

To be sure the only way is to look at the last triggers in mvb and not guessing at the siren internal battery back up cells.This case appears to be nothing more than voltage drop as the fault no longer exists